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Finding the radius of a brass ball using tension?

  1. Jan 25, 2009 #1
    1. The problem statement, all variables and given/known data

    One end of a wire is attached to a ceiling and a solid brass ball is tied to the lower end. The tension in the wire is 120N what is the radius of the brass ball.


    2. Relevant equations

    Brass Mass Density (kg/m^3) = 80470


    I have no clue how to solve this one, can anyone help?
     
  2. jcsd
  3. Jan 25, 2009 #2

    hage567

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    Start by drawing a free body diagram. You need to figure out the mass of the ball. How do you think you might do that?
     
  4. Jan 25, 2009 #3
    Could you find the mass of the ball by taking the tension and dividing it by the force of gravity? Would tension equal the weight force (Mass x Gravity) ?
     
  5. Jan 25, 2009 #4

    Doc Al

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    Staff: Mentor

    That's correct. Two forces act on the ball: The upward tension of the wire and the downward pull of gravity. They must balance, thus: T = mg.
     
  6. Jan 25, 2009 #5
    Ok I got that, but how do you find the radius of the ball from the volume that I calculated from the mass?
     
  7. Jan 25, 2009 #6

    hage567

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    What's the formula for the volume of a sphere?
     
  8. Jan 25, 2009 #7
    V = (4/3)πR^3 right?
     
  9. Jan 25, 2009 #8

    hage567

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    That's right.
     
  10. Jan 25, 2009 #9
    Alrite I get what to do now, thanks a ton =]
     
  11. Jan 25, 2009 #10

    hage567

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    You're welcome. :smile:
     
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